Seamless cloud interoperability is highly desired but not yet easily attainable in the current cloud solutions market. This work tackles one aspect of achieving cloud interoperability, namely, inter-cloud networking. We list the requirements and propose an inter-cloud networking architecture for a case of independent clouds owned by different entities and powered by different cloud management and network virtualization technologies. Then we validate the proposed architecture by describing an example of working implementation for Open Stack cloud powered by Open Daylight Open DOVE SDN solution. Finally, we compare our architecture to the existing solutions.